|Publication number||US7692389 B2|
|Application number||US 11/670,637|
|Publication date||Apr 6, 2010|
|Filing date||Feb 2, 2007|
|Priority date||Feb 4, 2006|
|Also published as||DE102006005128A1, DE102006005128B4, US20070194628|
|Publication number||11670637, 670637, US 7692389 B2, US 7692389B2, US-B2-7692389, US7692389 B2, US7692389B2|
|Original Assignee||Huettinger Elektronik Gmbh + Co. Kg|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (25), Non-Patent Citations (1), Referenced by (5), Classifications (8), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims priority under 35 U.S.C §119(a) to German Patent Application 10 2006 005 128.9-54, filed Feb. 4, 2006, the entire contents of which are hereby incorporated by reference.
The invention relates to a method and a device for matching the impedance of a variable load to the output resistance of a high frequency (HF) generator or source.
A load impedance, such as, for example, a plasma impedance, can be influenced by many parameters and therefore can vary over time. Thus, it can be difficult to match such a variable load impedance to an HF source. Automatic tuning circuits are sometimes used to improve matching of the load impedance in plasma thin-film technology for surface treatments. The automatic tuning circuits continuously follow changes in the load impedance in the plasma process.
Load impedances of laser excitation plasmas tend to fluctuate less than load impedances for plasma thin-film technologies Thus, fix match circuits can be used for load impedances of laser excitation plasmas. These fix match circuits are fixedly set for an acceptable load matching under standard burning (or ignited) conditions.
If the HF power from the source is supplied in a pulsed mode and the power is regulated by influencing the pulse duty factor, the load impedance fluctuation problem can be exacerbated since a periodic change between the impedance during the burning state and the impedance during ignition of the plasma also exists in the switched-on state.
Consequently, a compromise between optimization of the load matching and the ignition behavior is frequently set as matching. In addition, an ignition auxiliary circuit is usually used.
In one general aspect, the impedance of a variable load is matched to the output resistance of an HF generator by performing a first impedance matching for a first load impedance at a first frequency and performing a second impedance matching for a second load impedance at a second frequency. In this way, it is possible to automatically select between the two matchings according to the load impedance. That is, if a first load is present, a first impedance matching is performed on the first load, without any reactive elements in the matching circuit needing to be changed, and if a second load is present, a second impedance matching is performed with the same matching circuit, without needing to change any reactive elements. In particular, no separate triggering elements (such as, for example, variable elements or switching element) are required to change between the two matchings. Moreover, power that is output by an HF generator at a frequency higher than the fundamental frequency can be used in this way to ignite a plasma. An additional ignition aid is not needed.
Impedance matching can be carried out using a fixedly-set, non-variable matching device that is designed for two different load impedances at two different frequencies. The matching device uses two fixed, non-variable matchings, and does not require variable elements that are adjusted according to varying load impedance to produce matching. In this way, a matching for a high-impedance load impedance and a matching for a low-impedance load impedance can be provided.
The first frequency and the second frequency can be selected from the frequency spectrum of the HF generator. For example, the first frequency can be the fundamental frequency of the HF generator and the second frequency can be a harmonic. The power delivered at the fundamental frequency can be used for the ignited plasma operation (that is, the state in which the plasma is burning) and the power delivered at a harmonic can be used to ignite the plasma, and an optimal matching is provided in both cases by the fixed impedance matching. The matching device design can benefit from the fact that a plasma is easier to ignite with increasing frequency. For example, the industry frequency 13.56 MHz can be used as the fundamental frequency and the second harmonic at 40.68 MHz can be used as the harmonic.
The impedance matching can be carried out by means of a matching device whose structure is determined as follows. A first matching network is determined for a first impedance matching of a first load impedance at a first frequency. A second matching network is determined for a second impedance matching of a second load impedance at a second frequency. A minimal structure (that is, a basic circuit) containing at least both matching networks is determined, and the individual components of the minimal structure are replaced by LC arrangements that represent the respectively desired inductance or capacitance values for both frequencies. The LC arrangements can include series components, parallel components, or both series and parallel components.
The first and second load impedances can be predefined. A circuit that implements this method can be designed particularly simply. For the particular application of plasma processes, the first load impedance can be selected in the range of the impedance of an ignited plasma and the second load impedance can be selected in the range of the impedance of an unignited discharge section (that is, the gap between the electrodes in the plasma chamber).
Another aspect of the invention features a matching device that matches the impedance of a variable load to the output resistance of an HF generator. The matching device is designed for impedance matching of the first load impedance at a first frequency and for impedance matching of the second load impedance at a second frequency. The first matching or the second is selected automatically depending on the load impedance. Therefore, the matching device need not include separate switches or adjustment of components.
The first frequency can be the fundamental frequency of the HF generator and the second frequency can be a harmonic of the fundamental frequency. In this case, use can be made of the fact that the output circuit of HF generators frequently has a low Q factor so that this has a low spectral purity. The fundamental frequency and one or more harmonics are thus also provided by the HF generator. In plasma operation, the substantial power of the HF generator is drawn from the fundamental frequency. However, the power associated with a harmonic is frequently sufficient to ignite a plasma. In the case of impedance matching to a high impedance (for example, the impedance of an unignited discharge section) at a frequency that is higher than the fundamental frequency, the required ignition power can be delivered with good matching into a plasma chamber or to the electrodes of the plasma chamber.
The matching device can be fixedly set for matching a first and a second load impedance. Such a matching device provides good matching of a plasma load and also good matching during ignition of a plasma without there being any need for switches to enable variable load matching or variable capacitors that need to be driven by a controller and/or moved by motors. Furthermore, the matching device need not include ignition aids. The matching device can thus be implemented particularly cost-effectively.
In some implementations, the matching device can be designed with no variable elements nor switching elements.
The matching device can be embodied as a series and/or parallel circuit of a plurality of passive components, in particular, inductors and/or capacitors, whose matching behavior is different for two predefined frequencies. Compared to a conventional fix match matching that is only designed for one load at one frequency, individual reactance components are replaced by series or parallel combinations that represent different L (inductance) or C (capacitance) values depending on the frequency. As a result, additional degrees of freedom are provided, making it possible to design the matching device taking into account the overall matching in such a manner that matching can be improved or optimized at two different frequencies for two different impedances.
In another general aspect, a plasma process excitation arrangement includes an HF generator, a load, and an interposed matching device as described above. For some embodiments, the plasma process excitation arrangement provides impedance matching and ease of ignition of a plasma load.
The plasma process excitation arrangement can be designed for pulsed power supply with a duty factor adjustable by a power regulator. During such power regulation by means of the duty factor, oscillation of the output circuit builds up or decays rapidly so that steep flanks of the power signal are formed. This is achieved by a low Q factor of the output circuit, for example, a Q factor Q<3. A low-Q circuit can be implemented particularly cost-effectively and has a low spectral purity, and therefore such a low-Q circuit can be used for the matching device.
Further features and advantages are obtained from the following description with reference to the figures in the drawings, which show details, and from the claims. The features mentioned above and below can be utilized individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention
The HF generator 2 is designed for pulsed power supply to the load 8. The power delivered is adjusted by adjusting the pulse duty factor using a power regulator 15 within the HF generator 2. In order to ensure steep flanks (that is, an output signal from the HF generator 2 that has a steep slope), the output circuit 6 has a low Q factor (for example, a Q<3). As a result, the output circuit 6 can be constructed cost-effectively and simply. As a result of the low Q factor, however, the output circuit 6 has a low spectral purity so that power is also output at harmonics of the fundamental frequency, that is, at integer multiples of the fundamental frequency. The output power at frequencies above the fundamental frequency is lower than the output power at the fundamental frequency. If a discharge section is not ignited, however, the power output at a higher frequency is sufficient to ignite the plasma. In this case, the matching device 9 matches the load 8 to the output 7. Thus, no additional ignition aid is required. As soon as the plasma is ignited, the load impedance of the load 8 drops to a low value. In this case, the matching device 9 performs a matching to the output 7 since matching now takes place for the power output at the fundamental frequency. The matching for different load impedances thus takes place solely in dependence on the frequency and automatically and with only the use of passive components such as inductors and capacitors. Moreover, variable elements (such as variable capacitors) or switching elements are not required in the matching device 9.
The configuration of the matching device 9 can be determined, as explained below and with reference to
A minimal structure 13 (that is, a basic circuit) including a least both matching networks 11, 12 is then determined (as shown in
The individual components C1, C2 and L3 are replaced by LC arrangements that have the respectively desired L (inductance) or C (capacitance) value for both frequencies. Thus, in this embodiment, a series LC arrangement 14 replaces the capacitor C1, a series LC arrangement 17 replaces the inductor L3 and a capacitor 16 replaces the capacitor C2. The arrangements 14, 17, 16 together form the matching device 9, which is designed for load impedance matching of the two load impedances 8 a, 8 b two different frequencies.
It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.
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|U.S. Classification||315/111.21, 156/345.44, 315/111.51, 315/111.71|
|Cooperative Classification||H03H7/38, H05H1/46|
|Apr 23, 2007||AS||Assignment|
Owner name: HUETTINGER ELEKTRONIK GMBH + CO. KG, GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:KIRCHMEIER, THOMAS;REEL/FRAME:019192/0208
Effective date: 20070404
Owner name: HUETTINGER ELEKTRONIK GMBH + CO. KG,GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:KIRCHMEIER, THOMAS;REEL/FRAME:019192/0208
Effective date: 20070404
|Oct 1, 2013||FPAY||Fee payment|
Year of fee payment: 4